Make jsx-a11y lint rules strict by default

Created by: Ethan-Arrowood

Describe the bug

The jsx-a11y eslint rules are all set to warn by default. I believe accessibility is important and these rules should be set to error by default. Create-react-app is one of (if not the) most popular React application boilerplate tools. It is wonderful that jsx-a11y is included by default, but I think we can take it a step further and make the rules more strict (thus directly creating more accessible applications by default).

In addition, we should add documentation to the 'set up your environment' part that details how to override this back to warn if that is what developers want.

jsx-a11y provides a great base config we can extend from plugin:jsx-a11y/strict too to make this an easy fix.

I'd be more than happy to make the contribution if the maintainers give me the green light!